Ofdm transmitting and receiving systems and methods thereof

ABSTRACT

An orthogonal frequency division multiplexing (OFDM) transmission system is provided which includes a data processing unit which generates a transmission signal using a plurality of tones including a reserved tone, a storage unit which stores Peak Reduction Kernel information according to the type of data symbol, and a compensation unit which retrieves the Peak Reduction Kernel information according to the type of data symbol from the storage unit and causes the retrieved information to be carried by the reserved tone included in the transmission signal. Therefore, a Peak-to-Average Power Ratio (PAPR) can be efficiently compensated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 14/337,969,filed Jul. 22, 2014, which is a continuation of U.S. patent applicationSer. No. 12/527,202, filed Aug. 14, 2009, now U.S. Pat. No. 8,804,477,which is a National Stage of International Application No.PCT/KR2008/000788, filed Feb. 11, 2008, and claims priority from KoreanPatent Application No. 10-2007-0016824, filed on Feb. 16, 2007, in theKorean Intellectual Property Office, the disclosures of which areincorporated herein in their entireties by reference.

FIELD OF THE INVENTION

Systems and methods consistent with the present invention relate toorthogonal frequency division multiplexing (OFDM) transmitting andreceiving. More particularly, the present invention relates to OFDMtransmitting and receiving systems which select a Peak Reduction Kernelcorresponding to the type of data symbol and apply the selected PeakReduction Kernel in order to compensate a Peak-to-Average Power ratio(PAPR), and to methods thereof.

BACKGROUND OF THE INVENTION

OFDM schemes are utilized as standards for IEEE 802.11a, ETSI BRAN'SHYPERLAN 2, European digital audio broadcasting (DAB) and digital TVDVB-T. A conventional single carrier transmission scheme in whichinformation is carried by a single carrier causes interference betweensymbols to increase, so distortion also increases. Accordingly, anequalizer of a receiver must be complicated. In order to solve theseproblems of the conventional single carrier transmission scheme, OFDMschemes have been introduced.

OFDM schemes enable data to be transmitted using multi-carriers. SuchOFDM schemes are able to convert data symbols input in series intoparallel data symbols, to modulate each of the parallel symbols into aplurality of tone signals which are orthogonal to each other, and totransmit the modulated signals.

OFDM schemes have been widely applied to digital transmissiontechnologies, such as digital audio broadcasting (DAB), digitaltelevision, wireless local area network (WLAN) or wireless asynchronoustransfer mode (WATM). In particular, OFDM schemes maintain orthogonalitybetween tone signals, unlike conventional multicarrier schemes, so it ispossible to obtain optimum transmission efficiency during high speeddata transmission. Additionally, almost the whole available frequencyband can be utilized and multi-path fading can be reduced.

However, OFDM schemes have the disadvantage that OFDM signals exhibit ahigh Peak-to-Average Power Ratio (PAPR) due to modulation betweenmulti-carriers. The PAPR is essentially identical to a Peak-to-AverageRatio (PAR). Since data is transmitted using multi-carriers in OFDMschemes, the final OFDM signal has an amplitude equal to the sum ofamplitudes of individual carriers so that variation in the amplitudeincreases. Additionally, if phases of the individual carriers areidentical, a very large value may be obtained. Accordingly, the signalis out of the linear operating range of a high power linear amplifier,so distortion may occur during a linear amplifying operation.

Therefore, methods for reducing such a PAPR have been studied. Among themethods, a tone reservation method has been provided, in which a PeakReduction Kernel is carried and transmitted by a reserved tone, which isnot used to transmit data, among a plurality of tones for generatingmulti carrier signals, so as to compensate a PAPR.

In more detail, some of the tones are reserved in a frequency domain.After an initial value (for example, 0) is temporarily carried by thereserved tones, the reserved tones are converted into time-domainsignals, and a signal corresponding to a position having power greaterthan the permissible peak power is searched. A Peak Reduction Kernel forcompensating the position is then carried by the reserved tones, so thatthe PAPR can be compensated.

However, some of the reserved tones may be used for other purposes, forexample pilot transmission. Additionally, the position of reserved tonesused for other purposes may change according to a predetermined pattern.

The Peak Reduction Kernels has to be carried by reserved tones otherthan the reserved tones used for other purposes (hereinafter, referredto as additional data tones), so it is difficult to detect an optimumPeak Reduction Kernel. Additionally, the position of reserved tones intowhich Peak Reduction Kernels are to be inserted changes in various waysaccording to the type of symbols, and accordingly it is not easy todetermine a Peak Reduction Kernel according to the above change.

Therefore, there is a limitation to form a Peak Reduction Kernel, andthe PAPR reduction efficiency may thus be reduced.

SUMMARY

An exemplary embodiment of the present invention provides orthogonalfrequency division multiplexing (OFDM) transmitting and receivingsystems which select a Peak Reduction Kernel for Peak-to-Average Powerratio (PAPR) compensation according to the type of data symbols andapply the selected Peak Reduction Kernel so that a PAPR may beeffectively compensated even when the position of reserved tones usedfor other purposes changes, and methods thereof.

An exemplary embodiment of the present invention also providesorthogonal frequency division multiplexing (OFDM) transmitting andreceiving systems which detect the position of reserved tones withouttransmitting additional data so that the data symbols may be effectivelyrecovered, and methods thereof.

According to an aspect of the present invention, there is provided anorthogonal frequency division multiplexing (OFDM) transmitting systemincluding a data processing unit which generates a transmission signalusing a plurality of tones including reserved tones; a storage unitwhich stores Peak Reduction Kernel information according to the type ofdata symbols; and a compensation unit which retrieves from the storageunit information on a Peak Reduction Kernel matching the type of datasymbol to be transmitted and causes the retrieved information to becarried by the reserved tones contained in the transmission signal.

The data processing unit may set a position of an additional data tone,into which additional information is to be inserted and carried,according to a preset sequence, and may cause the type of data symbol tobe changed.

If there are a plurality of Peak Reduction Kernels corresponding to thetype of data symbols, the compensation unit may select one from amongthe plurality of Peak Reduction Kernels and may cause the selected PeakReduction Kernel to be carried by the reserved tones contained in thetransmission signal.

The data processing unit may include a data splitter which converts thedata symbols into a plurality of tone signals; an Inverse Fast FourierTransform (IFFT) processing unit which performs IFFT processing on theplurality of tone signals generated by the data splitter; and aparallel-to-serial converting unit which converts the plurality of tonesignals processed by the IFFT processing unit into a single serialsignal.

The data splitter may cause additional information to be carried by someof the reserved tones, excluding a normal tone which carries the datasymbol from the plurality of tones, to generate an additional data tonesignal, and may set a position of the additional data tone signalaccording to the type of data symbols in the preset sequence so as tochange the type of data symbol.

According to an aspect of the present invention, there is provided anorthogonal frequency division multiplexing (OFDM) receiving systemincluding a storage unit which stores position information of reservedtones, into which Peak Reduction Kernel information is inserted,according to the type of data symbols; and a reception data processingunit which, if a transmission signal is received from an OFDMtransmitting system, checks a position of a reserved tone matching thetype of data symbol represented by the received transmission signal, andrecovers the data symbol.

The reception data processing unit may check the type of data symbolaccording to the same sequence as used in the OFDM transmitting system,may retrieve position information of a reserved tone matching thechecked type from the storage unit, and may recover the data symbol.

According to an aspect of the present invention, there is provided anorthogonal frequency division multiplexing (OFDM) transmitting methodincluding generating a transmission signal using a plurality of tonesincluding reserved tones; retrieving information on a Peak ReductionKernel matching the type of data symbol to be transmitted, from astorage unit which stores Peak Reduction Kernel information according tothe type of data symbols; and causing the retrieved information to becarried by the reserved tones contained in the transmission signal andtransmitting the reserved tones with the retrieved information.

The generating may include setting a position of an additional datatone, into which additional information is to be inserted and carried,according to a preset sequence, and causing the type of data symbol tobe changed.

The retrieving may include, if there are a plurality of Peak ReductionKernels corresponding to the type of data symbols, selecting one fromamong the plurality of Peak Reduction Kernels according to the presetsequence.

The generating may include converting the data symbols into a pluralityof tone signals; performing inverse fast Fourier transform (TFFT)processing on the plurality of converted tone signals; and convertingthe plurality of transformed tone signals into a single serial signal.

The converting the data symbols may include setting a position of anadditional data tone which is to carry additional information amongtones excluding a normal tone which carries the data symbol from theplurality of tones, according to the type of data symbols in the presetsequence so as to change the type of data symbol.

According to an aspect of the present invention, there is provided anorthogonal frequency division multiplexing (OFDM) receiving methodincluding receiving a transmission signal from an OFDM transmittingsystem; detecting a position of a reserved tone matching the type ofdata symbol represented by the received transmission signal from astorage unit which stores position information of reserved tones, intowhich Peak Reduction Kernel information is inserted, according to thetype of data symbols; and recovering a data symbol carried by a normaltone according to the detected position of the reserved tone.

The detecting may include checking the type of data symbol according tothe same sequence as used in the OFDM transmitting system; andretrieving position information of a reserved tone matching the checkedtype from the storage unit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the invention will become and more readilyappreciated from the following description of the exemplary embodiments,taken in conjunction with the accompanying drawings of which:

FIG. 1 is a block diagram of an orthogonal frequency divisionmultiplexing (OFDM) transmitting system according to an exemplaryembodiment of the present invention;

FIGS. 2 to 5 are graphs illustrating a process for compensating aPeak-to-Average Power Ratio (PAPR) using a Peak Reduction Kernel,according to an exemplary embodiment of the present invention;

FIG. 6 is a block diagram of a data processing unit included in the OFDMtransmitting system of FIG. 1;

FIG. 7 is a block diagram of an OFDM receiving system according to anexemplary embodiment of the present invention;

FIG. 8 is a block diagram of a reception data processing unit includedin the OFDM receiving system of FIG. 7;

FIG. 9 is a flowchart illustrating an OFDM transmitting method accordingto an exemplary embodiment of the present invention; and

FIG. 10 is a flowchart illustrating an OFDM receiving method accordingto an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

Reference will now be made in detail to the present exemplaryembodiments of the present invention, examples of which are illustratedin the accompanying drawings, wherein like reference numerals refer tothe like elements throughout. The exemplary embodiments are describedbelow in order to explain the present invention by referring to thefigures.

FIG. 1 is a block diagram of an orthogonal frequency divisionmultiplexing (OFDM) transmitting system according to an exemplaryembodiment of the present invention. The OFDM transmitting system ofFIG. 1 includes a data processing unit 110, a compensation unit 120 anda storage unit 130.

The data processing unit 110 generates a transmission signal using aplurality of tones including a reserved tone. Specifically, the dataprocessing unit 110 modulates data symbols that are to be transmitted,generates a plurality of tone signals, and then converts the pluralityof tone signals into time-domain signals, so as to generate atransmission signal.

The reserved tone refers to a tone reserved to carry Peak ReductionKernel information or other additional information, as described above.Hereinafter, a reserved tone to carry additional information is referredto as an additional data tone.

Reserved tones may be disposed either randomly or in a predeterminedsequence, such as every third or fourth tone. For example, if (8 0 1024)tones exist, 4, 8, 12, 16, 20, 24, . . . , 4n-th tones are used asreserved tones.

Additionally, reserved tones disposed in regular positions among all thereserved tones may be used to transmit additional information. Theposition of reserved tones to transmit additional information, namely,the position of additional data tones may be determined according to thetype of data symbols.

Additional information, such as pilot information, is inserted into eachsymbol, and transmitted. Pilot information refers to information tocheck the signal quality and determine whether to perform channelcompensation, and may be shared with a receiver (not shown). Such pilotinformation is inserted into each respective data symbol andtransmitted, in order to equalize the power for transmitting datasymbols. Additionally, in order to prevent errors that occur when a tonesignal into which pilot information is inserted to be carried among aplurality of tone signals is lost, causing the tone signal not to betransmitted to a receiver, the position of a tone into which pilotinformation is inserted to be carried is changed according to the typeof symbols. Furthermore, system information to notify a coding rate ormodulation method is also inserted into each symbol and transmitted, inthe same manner as additional information described above.

The compensation unit 120 may insert Peak Reduction Kernels intoreserved tones obtained by excluding additional data tones and normaltones from all the tones. As described above, the position of availablereserved tones may be determined according to the type of data symbols.Accordingly, the compensation unit 120 retrieves information on a PeakReduction Kernel from the storage unit 130, as the most suitable for acurrent data symbol, and uses the retrieved information.

The storage unit 130 stores information on Peak Reduction Kernelsaccording to the type of data symbols. The information stored in thestorage unit 130 includes information contained in both the OFDMtransmitting system and an OFDM receiving system (not shown).

A system designer determines a Peak Reduction Kernel corresponding to areserved tone in a specific position. If 4, 8, 12, 16, 20, 24, 28, 32, .. . , 4n-th tones are used as reserved tones, and if the 4, 12, 20,28-th tones among the tones are used to transmit additional information,information regarding Peak Reduction Kernels when the 8, 16, 24, 32, . .. , 8n-th tones are used, is searched and stored in the storage unit130.

As shown in FIG. 1, the compensation unit 120 checks a current datasymbol and directly retrieves information on a Peak Reduction Kernelcorresponding to the current data symbol from the storage unit 130.However, this operation of the compensation unit 120 may be performed byan additional control unit (not shown), and the compensation unit 120may perform only functions of compensating a Peak-to-Average Power Ratio(PAPR) using the provided Peak Reduction Kernel.

FIGS. 2 to 5 are graphs illustrating a process by which the compensationunit 120 compensates a PAPR using a Peak Reduction Kernel, according toan exemplary embodiment of the present invention.

FIG. 2 is a graph illustrating a change in power of the time-domainsignals converted by the data processing unit 110. In FIG. 2, thetransmission signal may have peaks of various sizes. In this situation,a peak of the transmission signal may significantly increase in acertain position in which signals having the same phase among other tonesignals are synthesized. In FIG. 2, a peak 10 exceeds a threshold level50.

As shown in FIG. 3, the compensation unit 120 retrieves a Peak ReductionKernel from the storage unit 130 in order to compensate distortion. ThePeak Reduction Kernel is in the form of a signal having a compensationpeak 20, which coincides with the peak 10, and occurs in the position inwhich the peak 10 occurs. The compensation unit 120 inserts data, intowhich symbols of the compensation peak 20 are converted, into each ofthe reserved tones. Accordingly, the compensation peak 20 carried by thereserved tone and the peak 10 carried by the normal tone are offset toeach other, so that the distortion can be compensated.

The system designer may generate compensation signals according to thegradient algorithm, and store the generated compensation signals in thestorage unit 130 in advance. An initial value (for example, 0) iscarried by reserved tones currently available in the current datasymbol, so that the distortion is analyzed. Additionally, it is possibleto re-analyze a change in the distortion while controlling data thatwill be carried by the reserved tones. Therefore, it is possible togenerate a Peak Reduction Kernel most suitable for the current reservedtone.

FIG. 4 is a graph showing a form of a transmission signal in a frequencydomain. In FIG. 4, a tone having a center frequency f2 carries generaldata, and tones having center frequencies fI and f3 carry Peak ReductionKernels. FIG. 5 is a graph showing a PAPR compensated by the PeakReduction Kernel of FIG. 3. In FIG. 5, the peak 10 is reduced to lessthan the threshold level 50.

FIG. 6 illustrates the data processing unit 110 applicable to the OFDMtransmitting system of FIG. 1. The data processing unit 110 of FIG. 6includes a data splitter 111, an Inverse Fast Fourier Transform (IFFT)processing unit 112 and a parallel-to-serial converting unit 113.

The data splitter 111 causes data to be carried by a plurality of tones,converts the plurality of tones containing the data into a plurality oftone signals, and outputs the converted plurality of tone signals.Specifically, the data splitter 111 codes the data using a preset codingmethod, and performs symbol mapping on the coded data, so thatmodulation symbols are generated. The data splitter 111 then convertsthe generated modulation symbols into a plurality of parallel symbols,to generate a plurality of tone signals. To achieve this, the datasplitter 111 may include an encoder (not shown), a symbol mapper (notshown), a serial-to-parallel converter (not shown) or a pilot symbolinserter (not shown).

The IFFT processing unit 112 performs IFFT processing on the pluralityof tone signals generated by the data splitter 111, so that signals inthe frequency domain are converted into transmission signals in the timedomain.

The parallel-to-serial converting unit 113 converts the plurality oftone signals processed by the IFFT processing unit 112 into a singleserial signal.

The data splitter 111 reserves some of the plurality of tones. Thereserved tones do not carry general data. Additionally, some of thereserved tones carry additional information such as pilot informationaccording to a preset sequence, so the reserved tones are used asadditional data tones. In this situation, the position of the additionaldata tones may be determined according to the preset sequence.Accordingly, the type of data symbols may change.

For example, if the reserved tones include every third tone, 3, 6, 9,12, 15, 18, 21, 24, 27, 30, 33, 36, . . . , 3n-th tones among theplurality of tones are used as reserved tones. In this situation, thereare three types of data symbol. The first type is used when the(3n−2)-th reserved tones are used as additional data tones; the secondtype is used when the (3n−1)-th reserved tones are used as additionaldata tones; and the third type is used when the 3n-th reserved tones areused as additional data tones. Here, n is an integer. Optimum PeakReduction Kernels are generated according to each type and stored in thestorage unit 130, as described above.

The data splitter 111 may change the type of data symbols according tothe preset sequence. The sequence may be, for example, a sequence of1->2->3->1->2->3, a sequence of 1->3->2->1->3->2 or a sequence of1->2->3->2->1->2->3->2.

The configuration and operation of the data processing unit 110 areknown to those skilled in the art, so detailed description is omitted.

A process by which the compensation unit 120 retrieves data stored inthe storage unit 130 according to the type of data symbols will now bedescribed with the following equations.

If a set of additional data tones is P and if the type of additionaldata tones is K, P is represented by the following Equation 1.

Pi={Pi,I,Pi,2,Pi,3,Pi,4,Pi,5, . . . Pi,im} where i={I,2, . . .K}  [Equation 1]

In Equation 1, Pi indicates a set of i-th tones; Pi,j indicates aposition of the j-th component among the set of i-th tones; and imindicates the total number of components in the set of i-th tones.

The storage unit 130 may store M Peak Reduction Kernels represented bythe following Equation 2.

PRKi={PRKi,I,PRKi,2,PRKi,3, . . . PRKi,in} where i={1,2,3, . . .M}  [Equation 2]

In Equation 2, PRKi indicates an i-th Peak Reduction Kernel; and PRKi,jindicates a position of the j-th component of the i-th Peak ReductionKernel, that is, a compensation signal to be inserted into the j-threserved tone. Additionally, in indicates the total number of componentsin the i-th Peak Reduction Kernel.

The compensation unit 120 may select a Peak Reduction Kernel accordingto the following condition.

PRK _(y) where ∀ PRK _(y,j) ∉P _(i)  [Equation 3]

Accordingly, the compensation unit 120 may select a Peak ReductionKernel of which none of the components overlap with the position of eachof the set P of additional data tones. In this situation, if there are aplurality of Peak Reduction Kernels of which none of the componentsoverlap with the position of each of the set P, that is, if there are aplurality of Peak Reduction Kernels corresponding to the type of datasymbols, the compensation unit 120 may optionally select one from amongthe plurality of Peak Reduction Kernels. In this situation, theselection order is also known in the OFDM receiving system.

FIG. 7 is a block diagram of an OFDM receiving system according to anexemplary embodiment of the present invention. The OFDM receiving systemof FIG. 7 may receive a reception signal from the OFDM transmittingsystem of FIG. 1 and process the reception signal.

In FIG. 7, the OFDM receiving system includes a reception dataprocessing unit 210 and a storage unit 220.

The reception data processing unit 210 receives the transmission signalfrom the OFDM transmitting system and recovers the data symbol.

The storage unit 220 stores position information of reserved tonesaccording to the type of data symbols. The position information ofreserved tones provides notification on the position of reserved tonesinto which Peak Reduction Kernel information is inserted.

If the transmission signal is received, the reception data processingunit 210 reads position information of a reserved tone matching a datasymbol represented by the received transmission signal from the storageunit 220, and recovers the data symbol from the normal tone.

Specifically, the reception data processing unit 210 may check the typeof data symbol according to the sequence used by both the OFDMtransmitting system and OFDM receiving system. For example, if the typeof data symbol is set to change according to the sequence of1->2->3->1->2->3, the reception data processing unit 210 sequentiallyretrieves a plurality of pieces of position information of reservedtones matching each type from the storage unit 220. Accordingly, thereception data processing unit 210 may check tones other than thereserved tones, and recover the data symbol.

FIG. 8 is a block diagram of the reception data processing unit 210applicable to the OFDM receiving system of FIG. 7. The reception dataprocessing unit 210 of FIG. 8 may include a radio frequency (RF)processor 211, an analog-to-digital converter (ADC) 212, aserial-to-parallel converter 213, a Fast Fourier Transform (FFT)processing unit 214, an equalizer 215, a parallel-to-serial converter216, a symbol demapper 217 and a decoder 218.

The RF processor 211 down-converts a signal received via a receptionantenna to an intermediate frequency (IF) signal. The ADC 212 convertsthe down-converted signal into a digital signal, and theserial-to-parallel converter 213 converts the digital signal into aplurality of parallel signals.

The FFT processing unit 214 performs FFT processing on the plurality ofparallel signals. The equalizer 215 performs channel equalizationprocessing on the signals processed by the FFT processing unit 214. Theparallel-to-serial converter 216 receives the parallel signals from theequalizer 215 and converts the received signals into serial signals. Thesymbol demapper 217 demodulates the converted serial signals by ademodulation method corresponding to the modulation method in the OFDMtransmitting system. Subsequently, the decoder 218 decodes thedemodulated signals by a decoding method corresponding to the codingmethod in the OFDM transmitting system, and outputs the decoded signals.The above operations of the reception data processing unit 210 may beperformed with respect to tones other than the reserved tones read fromthe storage unit 220.

FIG. 9 is a flowchart illustrating an OFDM transmitting method accordingto an exemplary embodiment of the present invention. In FIG. 9, the OFDMtransmitting system modulates the data symbol into a plurality of tonesso that a transmission signal is generated (S910). In this situation,the plurality of tones include a plurality of reserved tones, and theposition of each of the plurality of reserved tones may change accordingto the preset sequence, so that the type of data symbols may alsochange.

After the transmission signal is generated, the OFDM transmitting systemchecks the type of current data symbol, and then retrieves a PeakReduction Kernel matching the type of current data symbol (S920).Notification on the type of current data symbol may be given byreferring to the preset sequence. Additionally, information regardingthe Peak Reduction Kernel may be acquired by retrieval from the storageunit 120 in which Peak Reduction Kernels have already been classifiedand stored according to the type of data symbols.

Accordingly, the OFDM transmitting system may cause the retrieved PeakReduction Kernel to be carried by the reserved tone and transmitted(S930). Therefore, the optimum Peak Reduction Kernel may be insertedinto the reserved tone even when the position of additional data toneschange, so it is possible to effectively reduce the PAPR.

FIG. 10 is a flowchart illustrating an OFDM receiving method accordingto an exemplary embodiment of the present invention. In FIG. 10, if atransmission signal generated by the method of FIG. 9 is received via areception antenna (S1010), the OFDM receiving system checks the type ofdata symbol of the received transmission signal according to the presetsequence. Subsequently, the OFDM receiving system retrieves positioninformation of a reserved tone matching the checked type from thestorage unit 220, so that the position of the reserved tone is detected(S1020).

The OFDM receiving system then detect the position of tones other thanthe reserved tone, namely, the position of normal tones or additionaldata, so that the data symbol may be recovered (S1030). Consequently, itis possible to effectively the data symbol without needing to receiveadditional information on the position of reserved tones.

As described above, according to the exemplary embodiments of thepresent invention, a Peak Reduction Kernel for PAPR compensation ispreviously stored, and the type of current data symbol is checked andthe previously stored Peak Reduction Kernel is selected and applied, soit is possible to compensate the PAPR effectively even when the positionof reserved tones changes. Additionally, it is possible to reduce thetime required to compensate the PAPR. Furthermore, it is possible toeffectively recover the data symbol even when additional informationproviding notification of the position of reserved tones is not receivedby a receiving system.

The foregoing exemplary embodiments and advantages are merely exemplaryand are not to be construed as limiting the present invention. Thepresent teaching can be readily applied to other types of apparatuses.Also, the description of the exemplary embodiments of the presentinvention is intended to be illustrative, and not to limit the scope ofthe claims, and many alternatives, modifications, and variations will beapparent to those skilled in the art.

The exemplary embodiments of the present invention are applicable to aEuropean digital broadcasting system which receives and transmitsbroadcasting streams using an OFDM technique.

What is claimed is:
 1. An orthogonal frequency division multiplexing(OFDM) transmitting system comprising: a storage configured to storeinformation regarding a position of reserved tones, the position of thereserved tones varying according to a type of data symbol; and aprocessor configured to identify information matching the type of datasymbol, and insert a signal for reducing a Peak-to-Average Power ratio(PAPR) into the reserved tones based on the information.
 2. The OFDMtransmitting system of claim 1, wherein the processor is configured tochange the type of data symbol by adjusting a position of an additionaldata tone according to a predetermined sequence, wherein additionalinformation is inserted into the additional data tone.
 3. The OFDMtransmitting system of claim 1, wherein the processor comprises: a datasplitter configured to convert the data symbol into a plurality of tonesignals; an Inverse Fast Fourier Transform (IFFT) processor configuredto perform IFFT on the plurality of tone signals; and aparallel-to-serial converter configured to convert the plurality of tonesignals processed by the IFFT processor into a single serial signal. 4.An orthogonal frequency division multiplexing (OFDM) receiving systemcomprising: a storage configured to store information regarding aposition of reserved tones, the position of the reserved tones varyingaccording to a type of data symbol; and a reception data processorconfigured to, in response to receiving a transmission signal from anOFDM transmitting system, identify information matching the type of datasymbol in the received transmission signal, and recover the data symbolbased on the information, wherein a signal for reducing aPeak-to-Average Power ratio (PAPR) is inserted into the reserved tones.5. The OFDM receiving system of claim 4, wherein the reception dataprocessor is configured to identify the type of data symbol in thereceived transmission signal, according to a same sequence as used inthe OFDM transmitting system, obtain the information matching theidentified type of data symbol from the storage, and recover the datasymbol based on the information.
 6. An orthogonal frequency divisionmultiplexing (OFDM) transmitting method comprising: identifyinginformation matching a type of data symbol, from information regarding aposition of reserved tones; and inserting a signal for reducing aPeak-to-Average Power ratio (PAPR) into the reserved tones based on theinformation, wherein the position of the reserved tones varies accordingto the type of data symbol.
 7. The OFDM transmitting method of claim 6,further comprising changing the type of data symbol by adjusting aposition of an additional data tone according to a predeterminedsequence, wherein additional information is inserted into the additionaldata tone.
 8. The OFDM transmitting method of claim 6, furthercomprising: converting the data symbol into a plurality of tone signals;performing inverse fast Fourier transform (IFFT) on the convertedplurality of tone signals; and converting the IFFT processed pluralityof tone signals into a single serial signal.
 9. An orthogonal frequencydivision multiplexing (OFDM) receiving method comprising: receiving atransmission signal from an OFDM transmitting system; identifyinginformation matching a type of data symbol in the received transmissionsignal from information regarding a position of reserved tones; andrecovering the data symbol based on the obtained information, whereinthe position of the reserved tones varies according to the type of datasymbol, and wherein a signal for reducing a Peak-to-Average Power ratio(PAPR) is inserted into the reserved tones.
 10. The OFDM receivingmethod of claim 9, wherein the identifying comprises: identifying thetype of data symbol in the received transmission signal, according to asame sequence as used in the OFDM transmitting system; obtaining theinformation matching the identified type of data symbol from thestorage; and recovering the data symbol based on the obtainedinformation.